Daniel Stashower was flipping through comic books in a friend’s tree house when he learned about a mysterious, unsuccessful plot to kill Abraham Lincoln. The tale of Lincoln’s narrow escape from an attempted murder in Baltimore before his 1861 inauguration appeared in a true-crime comic, and Mr. Stashower, then 13, was hooked.

His obsession never faded. Last night, Mr. Stashower took home the Edgar Award for Best Fact Crime at the Mystery Writers of America awards for his 2013 book “The Hour of Peril: The Secret Plot to Murder Lincoln Before the Civil War.” His account of the so-called Baltimore Plot details how detective Allan Pinkerton teamed up with the country’s first female private eye, Kate Warne to unravel a plot to kill Lincoln as he traveled by train from Springfield, Ill., to his inauguration in Washington D.C. Bestselling crime writer Harlan Coben called it “history that reads like a race-against-the-clock thriller.”